The use of a hand operated pointing device for use with a computer and its display has become almost universal. One form of the various types of pointing devices is the conventional (mechanical) mouse, used in conjunction with a cooperating mouse pad. Mechanical mice typically include a rubber-surfaced steel ball that rolls over the mouse pad as the mouse is moved. Interior to the mouse are rollers, or wheels, that contact the ball at its equator and convert its rotation into electrical signals representing orthogonal components of mouse motion. These electrical signals are coupled to a computer, where software responds to the signals to change by a ΔX and a ΔY the displayed position of a pointer (cursor) in accordance with movement of the mouse.
In addition to mechanical types of pointing devices, such as a conventional mechanical mouse, optical pointing devices have also been developed. In one form of an optical pointing device, rather than using a moving mechanical element like a ball, relative movement between an imaging surface, such as a finger or a desktop, and photo detectors within the optical pointing device, is optically sensed and converted into movement information.
Optical pointing devices typically include a light source for illuminating a surface to be imaged. For an optical mouse, the light source, such as a light emitting diode (LED), illuminates the surface under the mouse. While the mouse is moved, the LED is typically turned on at a constant frequency based on the frame rate of the optical motion sensor.
It is desirable to tightly control the range of illumination of the light source of optical pointing devices over the manufacturing process, operating modes, and operating conditions. For example, if several thousand optical pointing devices of a particular model are manufactured, it is preferable that all of the devices provide a similar level of illumination. It is also desirable that the light output be tightly controlled during operating modes, such as during different power saving modes, and in transitioning between the various operating modes. Existing optical pointing devices do not provide such control over the level of illumination.